HSPF2 is the heating counterpart to SEER2 — the seasonal heat a mini-split delivers divided by the electricity it uses, measured under the same 2023 Department of Energy test update (Appendix M1) that produced SEER2. As with cooling, the new HSPF2 numbers read lower than the old HSPF for identical equipment (roughly 8.8 HSPF ≈ 7.5 HSPF2), so don't compare an old spec sheet against a new one.
The federal minimum for a heat pump is 7.5 HSPF2, applied nationally with no regional split. Ductless mini-splits routinely beat it, landing in the 8 to 12+ HSPF2 range, with cold-climate models at the top. HSPF2 is the rating to weigh when the mini-split is your primary heat source — in a heating-dominated home a one- or two-point HSPF2 gain compounds across the season far more than the same gain in SEER2 would.
One number HSPF2 does not tell you is how the unit behaves on the coldest days. HSPF2 is a season-long average; a standard heat pump loses capacity as the temperature drops, while a cold-climate (hyper-heat) model is engineered to hold output near freezing and below. If winter performance matters, read the HSPF2 alongside the manufacturer's low-temperature capacity rating, not in place of it. And note 7.8 HSPF2 is the ENERGY STAR / common utility rebate threshold for ductless — above the federal floor, not the same as it.